hihocoder 1754

题目链接： https://hihocoder.com/problemset/solution/1327177

解题思路：

#include <bits/stdc++.h>
using namespace std;

typedef long long LL;
const int MAXN = 100005;
const LL MOD7 = 1e9+7;

LL C;
int n;
int a[64];
int cnt[64];

map<LL,int> ind2;
map<int,LL> pow2;

void init()
{
    pow2[0] = 1;
    ind2[1] = 0;
    for (int i=1;i<63;++i)
    {
        pow2[i] = pow2[i-1]*2;
        ind2[pow2[i]]=i;
    }
}

void work()
{
    cnt[0]=a[0];
    for (int i=1;i<63;++i)
    {
        cnt[i]=cnt[i-1]+a[i];
    }
    LL tmp=C;
    LL ans = 0LL;
    for (int i=62;i>=0;--i)
    {
        if (tmp>=pow2[i])
        {
            if (a[i]==1) {
                if (cnt[i]>=1) ans += pow2[cnt[i]-1];
            } else {
                ans += pow2[cnt[i]] - 1;
                break;
            }
            tmp-=pow2[i];
        }
    }
    printf("%lld
",ans);
}

int main()
{
    init();
#ifndef ONLINE_JUDGE
    freopen("test.txt","r",stdin);
#endif // ONLINE_JUDGE
    while ( scanf("%d%lld",&n,&C)!=-1 ) {
    LL d;
    for (int i=1;i<=n;++i)
    {
        scanf("%lld",&d);
        a[ind2[d]]=1;
    }
    work();
    }
    return 0;
}